The present invention relates to an automatically shiftable direction control valve for use with a tractor hydraulic system and more specifically relates to improvement in the hydraulic system and automatically shiftable direction control valve disclosed and claimed in the U.S. Pat. No. 3,543,516 granted to R. Treichel on Dec. 1, 1970.
The above-mentioned prior art patent discloses a direction control valve which is operative to automatically direct the exhaust of a single-acting function to the fluid reservoir and to direct the exhaust of continuously-acting or double-acting functions to a charging circuit for the main pump by blocking the exhaust from the reservoir and causing it to back up through a check valve into the charging circuit.
The disadvantage of the prior art is that a check valve is required and that it may hang up thus causing continuous feed of fluid in the charging circuit directly to reservoir resulting in there being insufficient fluid available to the main pump and to the low pressure priority functions.